title: The human minor histocompatibility antigen 1 is a RhoGAP.
abstract: The human minor Histocompatibility Antigen HMHA-1 is a major target of immune responses after allogeneic stem cell transplantation applied for the treatment of leukemia and solid tumors. The restriction of its expression to hematopoietic cells and many solid tumors raised questions regarding its cellular functions. Sequence analysis of the HMHA-1 encoding HMHA1 protein revealed the presence of a possible C-terminal RhoGTPase Activating Protein (GAP) domain and an N-terminal BAR domain. Rho-family GTPases, including Rac1, Cdc42, and RhoA are key regulators of the actin cytoskeleton and control cell spreading and migration. RhoGTPase activity is under tight control as aberrant signaling can lead to pathology, including inflammation and cancer. Whereas Guanine nucleotide Exchange Factors (GEFs) mediate the exchange of GDP for GTP resulting in RhoGTPase activation, GAPs catalyze the low intrinsic GTPase activity of active RhoGTPases, resulting in inactivation. Here we identify the HMHA1 protein as a novel RhoGAP. We show that HMHA1 constructs, lacking the N-terminal region, negatively regulate the actin cytoskeleton as well as cell spreading. Furthermore, we show that HMHA1 regulates RhoGTPase activity in vitro and in vivo. Finally, we demonstrate that the HMHA1 N-terminal BAR domain is auto-inhibitory as HMHA1 mutants lacking this region, but not full-length HMHA1, showed GAP activity towards RhoGTPases. In conclusion, this study shows that HMHA1 acts as a RhoGAP to regulate GTPase activity, cytoskeletal remodeling and cell spreading, which are crucial functions in normal hematopoietic and cancer cells.
authors.affiliation: Department of Molecular Cell Biology, Sanquin Research and Landsteiner Laboratory, Academic Medical Center, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Bart-Jan
authors.initials: BJ
authors.lastname: de Kreuk
authors.forename: Antje
authors.initials: A
authors.lastname: Schaefer
authors.forename: Eloise C
authors.initials: EC
authors.lastname: Anthony
authors.forename: Simon
authors.initials: S
authors.lastname: Tol
authors.forename: Mar
authors.initials: M
authors.lastname: Fernandez-Borja
authors.forename: Dirk
authors.initials: D
authors.lastname: Geerts
authors.forename: Jos
authors.initials: J
authors.lastname: Pool
authors.forename: Lothar
authors.initials: L
authors.lastname: Hambach
authors.forename: Els
authors.initials: E
authors.lastname: Goulmy
authors.forename: Peter L
authors.initials: PL
authors.lastname: Hordijk
mesh_terms: D000199:Actins / Q000378:metabolism; D001483:Base Sequence; D002465:Cell Movement; D017931:DNA Primers; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D015778:Minor Histocompatibility Antigens / Q000378:metabolism*; D016133:Polymerase Chain Reaction
chemical_list: D000199:Actins; D017931:DNA Primers; D020690:GTPase-Activating Proteins; D015778:Minor Histocompatibility Antigens; C085379:rho GTPase-activating protein